This invention relates generally to magnetic disk data storage systems, more particularly to magnetoresistive (MR) read heads, and most particularly to structures incorporating an Fe/FeSi/Fe synthetic antiferromagnetic (AFM) pinned layer and methods for making same.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In FIGS. 1A and 1B, a magnetic disk data storage systems 10 of the prior art includes a sealed enclosure 12, a disk drive motor 14, a magnetic disk 16, supported for rotation by a drive spindle S1 of motor 14, an actuator 18 and an arm 20 attached to an actuator spindle S2 of actuator 18. A suspension 22 is coupled at one end to the arm 20, and at its other end to a read/write head or transducer 24. The transducer 24 typically includes an inductive write element with a sensor read element (which will be described in greater detail with reference to FIG. 1C). As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the transducer 24 causing it to lift slightly off of the surface of the magnetic disk 16, or, as it is termed in the art, to xe2x80x9cflyxe2x80x9d above the magnetic disk 16. Alternatively, some transducers, known as xe2x80x9ccontact heads,xe2x80x9d ride on the disk surface. Various magnetic xe2x80x9ctracksxe2x80x9d of information can be read from the magnetic disk 16 as the actuator 18 causes the transducer 24 to pivot in a short arc as indicated by the arrows P. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art.
FIG. 1C depicts a magnetic read/write head 24 including a write element 26 and a read element 28. The edges of the write element 26 and read element 28 also define an air bearing surface ABS, in a plane 29, which faces the surface of the magnetic disk 16.
The write element 26 is typically an inductive write element. A write gap 30 is formed between an intermediate layer 31, which functions as a first pole, and a second pole 32. Also included in write element 26, is a conductive coil 33 that is positioned within an electrical insulator 34, such as a cured photoresistive material. As is well known to those skilled in the art, these elements operate to magnetically write data on a magnetic medium such as a magnetic disk 16.
The read element 28 includes a first shield 36, the intermediate layer 31, which functions as a second shield, and a read sensor 40 that is located between the first shield 36 and the second shield 31. The most common type of read sensor 40 used in the read/write head 30 is the magnetoresistive sensor. A magnetoresistive (MR) sensor is used to detect magnetic field signals by means of a changing resistance in the read sensor. When there is relative motion between the MR sensor and a magnetic medium (such as a disk surface), a magnetic field from the medium can cause a change in the direction of magnetization in the read sensor, thereby causing a corresponding change in resistance of the read element. The change in resistance can be detected to recover the recorded data on the magnetic medium.
One type of conventional MR sensor utilizes the anisotropic magnetoresistive (AMR) effect for such detection, where the read element resistance varies in proportion to the square of the cosine of the angle between the magnetization in the read sensor and the direction of a sense current flowing through the read sensor. Another type of MR sensor uses a phenomenon known as the giant magnetoresistive (GMR) effect. In such devices, the read sensor resistance is independent of the sense current direction, but varies in proportion to the cosine of the angle between the magnetizations of nearby layers. In a spin valve GMR sensor, two ferromagnetic layers are separated by a non-magnetic metal layer, sometimes referred to as a spacer layer. One of the ferromagnetic layers is a xe2x80x9cfreexe2x80x9d layer, whose magnetization can be moved by external magnetic fields. The other ferromagnetic layer is a xe2x80x9cpinnedxe2x80x9d layer whose magnetization is set in a particular direction and resistant to changes of that direction by external magnetic fields. This pinning is typically achieved with an exchanged-coupled antiferromagnetic (AFM) layer adjacent to the pinned layer.
In FIG. 2, a view taken along line 2xe2x80x942 of FIG. 1C (i.e., perpendicular to the plane 29 and therefore perpendicular to the air bearing surface ABS) illustrates the structure of the read sensor 40, in the form of a spin valve read sensor of the prior art. The spin valve read sensor 40 includes a free layer 42, a non-magnetic metal spacer layer 44, and a pinned layer 46 which together form the sensing layers 47. In addition, the read sensor 40 includes an antiferromagnetic (AFM) pinning layer 48 that pins the magnetization of the adjacent pinned layer 46. The spin valve read sensor 40 is supported by a substrate 50 (which can be the first shield 36) and a buffer layer 52, while a capping layer (not shown) can be provided over the AFM layer 48. Although not shown in FIG. 2, leads, typically made from gold or another low resistance material, route a sense current from a current source to the spin valve read sensor 40, while signal detection circuitry detects changes in resistance of the read sensor 40 as it encounters magnetic fields.
The free and pinned layers 42 and 46 are typically made from a soft ferromagnetic material such as Permalloy, while the non-magnetic metal spacer layer 44 can be formed of copper (Cu). The pinning layer 48 is formed of an antiferromagnetic (AFM) material that is used to set the magnetic direction of the pinned layer 46, preventing the magnetization of the pinned layer 46 from rotating under most operating conditions. The antiferromagnetic material of the pinning layer 48 can be, for example, a manganese (Mn) alloy such as iron-manganese (FeMn) or an oxide such as nickel-oxide (NiO).
The function of the pinned layer 46 can be better understood with reference to the magnetization directions depicted in FIG. 2. The pinned layer 46 is magnetized as indicated by the arrow 43. Alone, the free layer 42 may have an initial magnetization as indicated by the dashed arrow 45. However, in a spin valve such as that depicted in FIG. 2, there is a magnetostatic coupling of the pinned layer 46, a ferromagnetic exchange coupling through the non-magnetic metal spacer layer 44, and a field generated by the sense current I. Thus, the free layer 42 can have an actual magnetization direction as illustrated by the arrow 41 (which appears as a point in FIG. 2 because it is directed into the plane 29), which is due to the sum of the initial magnetization 45, the magnetostatic coupling of the pinned layer 46, the ferromagnetic exchange coupling though the spacer layer 44, and the field generated by the sense current I.
Other spin valve read sensors have been developed which use a multilayer pinned layer in place of the single pinned layer 46 of FIG. 2. Such a pinned layer 46xe2x80x2 is shown in FIG. 3, formed of a first ferromagnetic (FM) layer 54 that is separated from a second FM layer 55 by a non-magnetic spacer layer 56. Specifically, such a read sensor has been developed with the first and second FM layers formed of cobalt and the spacer layer formed of ruthenium (Ru). The magnetization 57 of the first FM layer is set in a first direction, while the magnetization 58 of the second FM layer is set in a second direction that is substantially antiparallel to the first direction. The two FM layers are strongly antiferromagnetically coupled in an antiparallel orientation, and their magnetizations are pinned by the pinning layer 48. Thus, the magnetization of the pinned layer 53 is significantly resistant to perturbation by the external magnetic fields used to change the magnetization 41 of the free layer 42.
FIG. 4 is a graph of the saturation field (Hs) of a spin valve read sensor incorporating a pinned layer such as that shown in FIG. 3, as it varies with thickness of the spacer layer. The saturation field is directly correlated with the coupling strength between the first and second FM layers, and is an indicator of read sensor performance. As can be seen from the graph, the saturation field follows an oscillation referred to as Ruderman-Kittel-Kasuya-Yosida (RKKY) oscillation, with high saturation fields being experienced only with small spacer layer thicknesses. For example, saturation fields above 2,000 oersteds can be achieved only with thicknesses smaller than about 8 angstroms. Further, as the steep slope of the depicted curve below about 8 angstroms indicates, very small variances in thickness will result in relatively large differences in saturation field. Thus, fabrication of a spin valve using the pinned layer 46xe2x80x2 of FIG. 3 requires very precise thickness control. This requirement can add to the cost of read sensors, for example through requiring more expensive control equipment to ensure proper thicknesses or lower yields due improper thicknesses.
Thus, what is desired is an improved pinning layer for use in magnetoresistive devices, such as spin valve devices. In particular, a pinning layer that maximizes performance while being easier and less expensive to manufacture is needed.
The present invention provides a magnetoresistive device and method for making the same that provides high performance and can be fabricated with low cost and low complexity. Specifically, a synthetic AFM layer is provided that can be used as a pinned layer of a spin valve read sensor and can be fabricated with a spacer layer having larger thicknesses, and a larger range of thicknesses, than in the prior art, while still providing high levels of spin valve performance. These larger thicknesses and larger range of thicknesses allow for easier control of the spacer layer fabrication, and therefore lower cost of producing larger quantities of magnetoresistive devices that include the synthetic AFM layer.
According to an embodiment of the present invention, a magnetoresistive device includes a synthetic antiferromagnetic (AFM) layer having a first ferromagnetic (FM) layer including iron (Fe) and a second FM layer including Fe. The first FM layer and second FM layer are separated by an intermediate layer including Fe and silicon (Si). The first FM layer has a magnetization that is pinned in a first direction, while the second FM layer has a magnetization that is pinned in a second direction that is substantially antiparallel to the first direction. The magnetoresistive device further includes a spacer layer overlying the synthetic AFM layer, with the second FM layer being proximate the spacer layer and the first FM layer being distal the spacer layer. Additionally, the magnetoresistive device includes a free layer overlying the spacer layer and formed of a ferromagnetic material. In a particular embodiment, the intermediate layer includes an iron-silicon alloy, i.e., iron-silicide. A magnetoresistive device having such a synthetic AFM layer provides high saturation fields, while incorporating a spacer which can have a thickness that is easy to fabricate.
In another embodiment of the present invention, a system for reading from and writing to a magnetic medium includes a write element and a read element. Specifically, the read element includes a spin valve magnetoresistive device having a synthetic antiferromagnetic (AFM) layer. The synthetic AFM layer includes a first FM layer, consisting essentially of iron (Fe), separated from a second FM layer, consisting essentially of Fe, by a first spacer layer that consists essentially of Fe and silicon (Si). In particular embodiments, the first space layer can consist essentially of iron-silicide (FeSi). The system for reading from and writing to a magnetic medium can also include a medium support that is capable of supporting a medium and moving the medium in relation to a read/write head that includes the write element and the read element. Also included can be a read/write head support system for suspending the read/write head above the medium. With the synthetic AFM pinned layer of the present invention, a magnetic data storage system can render high performance while keeping fabrication costs low.
In yet another embodiment of the present invention, a method of forming a magnetoresistive device, includes providing a substrate and forming a synthetic AFM layer having a first iron (Fe) layer and a second iron (Fe) layer separated by an iron-silicide (FeSi) layer. The formation of the synthetic AFM layer can include depositing a first Fe initial layer over the substrate, depositing a silicon (Si) layer over the first Fe initial layer, and depositing a second Fe initial layer over the Si layer. The method also includes heating the first Fe initial layer, the Si layer, and the second Fe initial layer until material from at least one of the first Fe initial layer and the second Fe initial layer propagates into the Si layer to transform the Si layer into the FeSi layer. Alternatively, a combined layer of Fe and Si can be deposited on a first Fe initial layer and covered with a second Fe initial layer. The combined layer is heated to form the FeSi layer. A pinning layer can also be formed between the substrate and the synthetic AFM layer. This method produces a read sensor that experiences high saturation fields while requiring reduced spacer layer thickness control during fabrication. Also, the formation of the iron-silicide spacer layer can be conducted at temperatures and for time periods consistent with the field annealing procedure of the pinning layer.
These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following descriptions of the invention and a study of the several figures of the drawing.